Color television cameras using solid-state image pickup devices are in widespread use. General people can easily pick up images. A color television camera increased in sensitivity for night image pickup is also provided.
A monitoring color television camera is also increased in resolution and sensitivity. A large number of color television cameras are set in a town for crime prevention and are actively used.
Although in both the color television camera and the monitoring color television camera almost no deficiency is felt in image pickup in the daytime, during night image pickup, however, if an illumination lamp or signal lamps of a traffic signal in an intersection or the like are present in an image pickup region of the color television cameras, there is a deficiency that electronic shutter controlling means of a solid-state image pickup device or an automatic gain control circuit is actuated by a signal level of the lamp and a dark part is not faithfully reproduced, although a signal of the illumination lamp, the signal lamps of the traffic signal, or the like is controlled at a proper level.
If it is attempted to improve dark part reproducibility, a video of the illumination lamp, the signal lamps of the traffic signal, or the like changes to a white solid. Even if the video is corrected in terms of a circuit by white compression, a knee characteristic, there is a limit in the correction.
Therefore, Japanese Patent Laid-Open No. 2009-55504 of Patent Literature 1 discloses an invention of a monitoring camera apparatus that can perform monitoring in the daytime and at night and can monitor even a monitoring target having steep luminous intensity distribution, intense directivity, and high luminance such as an LED traffic signal without causing white void (white solid) in a picked-up image and while keeping color reproducibility.
An optical filter having a region in which an object light amount from a monitoring region is further attenuated than the other portions is automatically inserted into or retracted from an optical path between a lens and an image pickup device in the monitoring camera apparatus according to a video signal level in the monitoring camera apparatus. The monitoring camera apparatus can pick up an image without causing deterioration in color reproducibility due to white void in a monitoring image.
Therefore, the optical filter disposed in the optical path between the lens and the image pickup device includes a filter region of a glass or plastic substrate where an ND filter is absent in a frame body and a filter region where an ND filter vapor-deposited with a light absorbing or reflecting material or the like is present on the surface of a plastic substrate or the like. The optical filter is mechanically slid in the longitudinal direction of the optical filter to thereby enable the filter regions, which can partially attenuate a light amount, to intrude into and retract from the optical path.